Replies

1. 
   SgianDubh | Dec 19, 2004 09:48pm | #1

   Ah Scott, almost certainly you used PVA glue to assemble the boards. That most likely being the case you're witnessing one of PVA's characteristics, i.e., creep as exhibited in this form.

   PVA never sets solid. There's always a bit of give, so if your boards moved a bit, so did the glue. The result is a slight misalignment as you describe, and oftentimes the alternative result is a row of pimples along the glue line. The latter is often caused where a glued up panel using PVA shrinks due to moisture loss after assembly-- moisture cycing. The wood shrinks, but the glue doesn't.

   A similar effect is seen when a dry assembled panel using PVA takes on moisture and later dries-- a row of pimples, again moisture cycling.

   Another form of creep can be seen in laminated bent wood or man made board structures. If PVA is used there is a tendency for the lamination to straighten after removal from the former. And the straightening continues in service unless the laminated item is locked at either end in some way. Laminates will also slip across their width if continuous stress is applied to one edge.

   To avoid creep, use a non-creeping glue, such as Scotch glue-- hot or cold liquid, polyurethane, urea formaldehyde, urea resorcinol, epoxy resin and so on, but all of these glues also have their strengths and weaknesses which might include fussiness of preparation, shelf life, pot life, lack of gap filling ability, poor shock resistance, etc.. PVA is a very useful all-purpose glue, within its limitations. Slainte.

   RJFurniture

1. 
   PaDutchman | Dec 19, 2004 10:23pm | #2

         Thanks for the reply. I used Titebond II. I forgot to note that I also used biscuits so that the wood wouldnt move during glueup. Am I understanding you to say that the "edge" I feel is glue?

1. 
   SgianDubh | Dec 20, 2004 03:14am | #3

   Scott, that's the usual result of creep in glued up panels, a row of pimples. It might be what you were feeling, although I've seen one plank creep slightly out of line as well quite often.

   The biscuits you used have just enough give to allow the misalignment type of creep. Here are a couple of things to watch for when using biscuits in edge joinery along with PVA and other water based glues.  Don't hurry after the joinery to get to the preparation and polishing stage.

   Leave the planks to settle for a week or two. Water introduced at gluing causes the biscuits and surrounding wood to swell which will take a few days to go back down. Biscuits can show as a row of elliptical dimples under polish if not allowed time. The whole glued joint, not just the area around the biscuits needs some time to settle to reduce the chance of the row of pimples syndrome. This latter applies to classic edge joinery using no alignment aids too.

   Titebond II is a PVA glue just confirm that. Slainte.

   RJFurniture

   Edited 12/19/2004 7:15 pm ET by Sgian Dubh

1. 
   PaDutchman | Dec 20, 2004 04:03pm | #4

         A final thank you for all the help. I'll try your tips for the next project and see how everything turns out!

2. 
   PlaneWood | Dec 20, 2004 05:46pm | #5

   Scott -

   I once did a PVA glue up of cherry for a king sized bed headboard.  After scraping and sanding and getting it smooth, I came out the next morning and the glue lines had raised.  Smoothed it down again.  Next day, same thing.  This went on for 2 weeks.  I finally got tired of it and stained and finished it out.  After a week under the finish the glue lines had shrunk.  I can still see the shrunken lines but the wife thinks I'm crazy cause she can't see them.  One of the few pieces she has complimented me on.

   I think it's the moisture in the glue causing the wood to swell at the glue line.  I've used epoxy and not had this happen.  I'll not use Titebond on future large glue up's.

   PlaneWood by Mike_in_Katy (maker of fine sawdust!)
   PlaneWood

1. 
   SgianDubh | Dec 20, 2004 06:38pm | #6

   Hot and humid Houston has that effect on PVA glues Mike. That's why I virtually gave up using the stuff when I lived there. Slainte.RJFurniture

2. 
   PaDutchman | Dec 20, 2004 11:37pm | #8

         Thanks for the additional input. Maybe I need to rethink my glue choices for my next project. I wasn't aware of the PVA issues with moisture until you all enlightened me. I've used the Weldwood resin glue in the past with no problems. Do any of you have a favorite glue for edge gluing?

   Thanks

   Scott

1. 
   PlaneWood | Dec 21, 2004 05:38am | #9

   I've been using the ready made hide glue lately with excellent results.  Franklin brand I think.  Don't buy it in large quantities though.

   PlaneWood by Mike_in_Katy (maker of fine sawdust!)PlaneWood

1. 
   PaDutchman | Dec 21, 2004 08:19pm | #10

         Once again, thanks for taking the time to answer my inquiry!

   Thanks

   Scott

3. 
   JohnWW | Dec 20, 2004 07:11pm | #7

   PVA glue creeping out of the joint is one possibility, but it seems to be something of a random event, I've only seen it happen a few times in many years of woodworking, and there was nothing unique about the times it did occur.

   A second possibility, that is rarely mentioned, is that one of the boards was flat sawn and the other was quarter sawn.  A flat sawn board will shrink or expand twice as much in thickness as a quarter sawn board for the same amount of moisture change.  If the moisture content of the wood changed by 10%, the difference in shrinkage is enough to cause a one to two hundredths of an inch step between the two boards which would be quite obvious.

   John W.